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New Member

Multicast source-only Network

In a switched environment (cat6500), there is a multicast server sending multicast data, but there is no clients. IGMP snooping is enabled on this segment. Every 5 minutes, I see flooding of multicast traffic to all switch ports belonging to the same vlan as multicast server, which lasts for few seconds. Is there a way to stop this periodic multicast flooding to other switch ports?

  • Other Network Infrastructure Subjects

Re: Multicast source-only Network

Try enabling igmp fastleave and see if it helps.

set igmp fastleave enable

Does the switch mac-address-table show dynamically learnt multicast mac-addresses corresponding to the access ports?

New Member

Re: Multicast source-only Network

Yes, it does. It shows them under 'show cam static'. For about 5 mins, you can see that all L2 mac addresses (corresponding to L3 GDA) are on the CAM table. During this time multicast doesn't flow on the ports that do not join those groups. After 5 min period, all the entries corresponding to multicast groups on the CAM table are removed for few secs, and then burst of multicast traffic can be seen on the ports that have not joined, and then everything gets back to normal. I've seen on the cisco TAC web-site something called 'multicast source only subnets' on which it says that cam entries for multicast entries gets flushed every five minutes, and then flooded to all ports momentarily till entries are relearned again, I.E. they point to the multicast router port only.

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